1. Field of the Invention
The present invention relates to a tilting type steering apparatus for enabling adjustment of a level of a steering wheel which steers a car.
2. Related Background Art
A level adjusting apparatus for a steering wheel called a tilting type steering apparatus to permit to change a level of a steering wheel depending on a physical feature of a driver or an attitude of the driver has been known by Japanese Utility Model Publication No. 62-18121.
The tilting type steering apparatus may be constructed as shown in FIG. 6. A steering shaft 2 which is rotated by manipulating a steering wheel 1 fixed at a top (rear) end extends through a steering column 3, which is pivotally supported around a horizontal shaft 4 to a car body at a bottom (front) end thereof and vertically movably supported to the car body at a top end thereof.
An arcuate slot 6 centered at the horizontal shaft 4 vertically extends in a fixed bracket 5 which is fixed to the car body below a dash board. An elevation bracket 7 (see FIGS. 7 to 9 to be explained later) made of a metal plate having a sufficient rigidity which is bent is fixed by welding to the top of the steering column 3 at a portion facing the fixed bracket 5.
A tilt bolt extends through holes 8 (see FIGS. 7 to 9) formed in the elevation bracket 7 and the slot 6. A width d of a head 21 (see FIGS. 7 to 9) of the tilt bolt 9 is selected to be sufficiently larger than a width W.sub.6 of the slot 6 (d&gt;W.sub.6) so that the head 21 does not pass through the slot 6. The head 21 is engaged in a manner to permit only elevational movement but prevent the rotation of the slot 6. The binding and the release of a tilt nut 10 (FIGS. 7 to 9) meshed with a male screw at an end of the tilt bolt 9 are carried out by manipulating a tilt lever 11.
In order to adjust the level of the steering wheel 1, the tilt bolt 9 is moved along the slot 9 of the fixed bracket 5 while the tilt nut 10 is loosened, and the tilt nut 10 meshed with the tilt 9 is bound by the tilt lever 11.
For example, when the tilt nut 10 is bound while the tilt bolt 9 is moved to the top end of the slot 9, the steering wheel 1 is in a position shown by a solid line in FIG. 6, and when the tilt nut 10 is bound while the tilt bolt 9 is moved to the bottom end of the slot 6, the steering wheel 1 is at a descended position as shown by a chain line in FIG. 6.
In order to prevent inadvertent movement of the level of the steering wheel 1 after the adjustment of the level of the steering wheel 1, Japanese Utility Model Publication No. 59-43163 discloses a structure as shown in FIGS. 7 and 8. A fixed gear 13 is screwed to an outer surface of one of a pair of vertical plates 12 which form a fixed bracket 5.
A lock plate 14 is provided between the fixed gear 13 and the tilt nut 10 meshed with the end of the tilt bolt 9. An elevation corrugated plate 17 and a fixed corrugated plate 16 of a wash board shape, which mesh with each other, are formed on an inner surface of the lock plate 14 and an outer surface of the fixed gear 13. The lock plate 14 is resiliently urged to the fixed gear 13 by a compression spring 15 provided between the tilt nut 10 and the lock plate 14.
When the tilt nut 10 is moved leftward in FIG. 8 to fix the steering wheel 1 after the adjustment of the level thereof, the lock plate 14 is inhibited to move rightward in FIG. 8. As a result, the lock plate 14 is inhibited from the elevation while the fixed corrugated plate 16 and and the elevation corrugated plate 17 are meshed with each other. Accordingly, the tilt bolt 9 which extends through the lock plate 14 is inhibited from the elevation so that the inadvertent change of the level of the steering wheel is prevented.
On the other hand, Japanese Laid-Open Utility Model Application No. 63-32963 discloses a structure as shown in FIG. 9. A lock member 18 is provided between a tilt nut 10 and a fixed bracket 5, and an elevation corrugated plate 17 formed on the lock member 18 is engageable with a fixed corrugated plate 16 formed on an outer surface of a fixed bracket. Projections 19 are formed at top and bottom ends of the inner surface of the lock member 18 so that the rotation of the lock member 18 is prevented by the engagement of the projections 19 with the slot 6. A compression spring 20 is provided between an outer surface of an elevation bracket 7 and the lock member 18 to apply a biasing force to the lock member 18 for releasing the meshing of the fixed corrugated plate 16 and the elevation corrugated plate 17.
When the tilt nut 10 is moved rightward in FIG. 9 to fix it after the adjustment of the level of the steering wheel, the lock member 18 is inhibited from the leftward displacement. As a result, the lock member 18 is prevented from the elevation while the fixed corrugated plate 16 and the elevation corrugated plate 17 are meshed with each other. Accordingly, the tilt bolt 9 which extends through the lock member 18 is inhibited from the elevation so that the inadvertent change of the level of the steering wheel is prevented.
In the structure shown in FIGS. 7 and 8 of the prior art structures described above, the lock plate 14 is kept resiliently urged to the fixed gear 13 by the resilient force of the compression spring 15. As a result, when the lock plate 14 is elevated to adjust the level of the steering wheel, the elevation corrugated plate 17 rides over the fixed corrugated plate 16 so that a person (driver) who manipulates the tilting steering apparatus feels uncomfortable feeling.
On the other hand, in the structure shown in FIG. 9, when the tilt nut 10 is loosened, the lock member 18 is urged leftward by the spring force of the compression spring 20 so that the elevation corrugated plate 17 formed on the lock member 18 and the fixed corrugated plate 16 formed on the outer surface of the fixed bracket 5 tend to be disengaged. Thus, noise will not be generated when the level of the steering wheel is adjusted so long as the dimensional accuracy of the components is assured.
In actual, however, it is difficult to secure the dimensional accuracy of the components in view of the cost, and when the level of the steering wheel is adjusted while the tilt nut 10 is loosened, noise may be generated from the meshing area of the corrugated plates 16 and 17 if a retract amount of the elevation corrugated plate is short.
In the prior art tilting steering column apparatus, the pair of vertical plates 12 which form the fixed bracket 5 are parallel to each other. In order to permit smooth elevation of the elevation bracket 7 within the vertical plates 12 when the level of the steering wheel is adjusted, a spacing D between the inner surfaces of the vertical plates 12 is selected to be sufficiently larger than a width W.sub.7 of the elevation bracket 7 (D&gt;W.sub.7) as exaggeratedly shown in FIG. 10.
When the tilt nut 10 is bound to fix the level of the steering wheel, the spacing D is reduced because of the elastic deformation of the vertical plates 12 so that the inner surfaces of the vertical plates 12 and the outer surfaces of the elevation bracket 7 come closer to each other. On the other hand, when the tilt nut 10 is loosened to adjsut the level of the steering wheel, a distance L between the tilt nut 10 and a head 21 of the tilt bolt 9 is expanded and the vertical plates 12 are elastically deformed so that the inner surfaces of the vertical plates 12 and the outer surfaces of the elevation brackets 7 are moved apart from each other and a clearance 42 is formed between the inner surface of the vertical plate 12 facing the tilt nut 10 and the outer surface of the elevation bracket 7 as exaggeratedly shown in FIG. 10.
On the other hand, when the meshing of the fixed corrugated plate 16 and the elevation corrugated plate 17 are to be completely disengaged, it is necessary to form a clearance 43 between the corrugated plates 16 and 17 as exaggeratedly shown in FIG. 10. No problem will arise if the clearance 43 is formed between the fixed and elevation corrugated plates 16 and 17 when the tilt nut 10 is loosened, but in actual, a clearance 42 is first formed between the inner surface of the vertical plate 12 and the outer surface of the elevation bracket 7 and then the clearance 43 is formed. This is due to the fact that the elasticity of the vertical plates 12 is larger than that of the compression spring 20.
The above problem may be avoided if the elasticity of the vertical plates 12 is smaller than that of the compression spring 20 but a sufficiently large elasticity is required for the vertical plates 12. In addition, the increase of the elasticity of the compression spring 20 leads to the increase of the manipulation force of the tilt nut 10. Accordingly, it is difficult to make the elasticity of the vertical plates 12 smaller than the elasticity of the compression spring 20.
Further, when a stroke of the distance L between the tilt nut 10 and the head 21 of the tilt bolt 9 due to the manipulation of the tilt nut 10 is increased, the manipulation for adjusting the level of the steering wheel is rendered troublesome and it is difficult to adopt it.
On the other hand, in the structure shown in FIG. 9, when the tilt nut 10 is in the loose position, the meshing of the corrugated plates 16 and 17 is disengaged by the spring force of the compression spring 20. Accordingly, noise is not generated when the level of the steering wheel is adjsuted but it is hard to mesh the corrugated plates 16 and 17 with each other when the tilt nut is bound to fix the level of the steering wheel.
Namely, in the structure shown in FIG. 9, when the tilt nut 10 is bound while the peaks of the corrugated plates 16 and 17 face each other, the lock member 18 is urged to the outer surface of the fixed bracket 15 while the peaks abut against each other. When a vertical force is applied to the steering wheel under this condition, the level of the steering wheel will easily be changed.
Particularly in the structure shown in FIG. 9, the projections 19 formed on the lock member 18 are engaged with the slot 6 of the fixed bracket 5 in order to prevent the rotation of the lock member 18 but a certain clearance must exist at the engagement in order to permit the smooth elevation of the lock member 18. Because of this clearance, it is unavoidable that the lock member 18 is rotationally displaced even if it is small. When the lock member 18 is displaced, the apex of the fixed corrugated plate 16 and the apex of the elevation corrugated plate 17 are in a twisted positional relation so that the apexes of the corrugated plates 16 and 17 may easily abut against each other.
In the structure shown in FIGS. 7 and 8 as well as the structure shown in FIG. 9, since the coiled compression springs 15 and 20 are used to press the lock plate 15 or the lock member 18, the axial dimension (lateral direction in FIGS. 7 and 8) of the tilt bolt 9 increases.